In the production of non-woven fabrics, such as spunbond and meltblown fabrics, molten polymer is extruded through a many holed die, or spinneret. The fibers are drawn by an air current and then collected in a random array to form a web of fibers. The web thus formed is then bonded by heating it to soften the polymer fibers and then passing the web through smooth or engraved calender rollers to bond the fibers. Bonding improves the strength of the non-woven fabric over non-bonded materials.
In many cases, the bonding process governs the speed at which a producer can run a line producing non-woven fabrics. The time that the web requires between the nips in the calendering process is controlled by the properties of the polymer in the fibers that make up the web, as well as the temperature and pressure of the calender rolls.
In certain applications it is desirable to combine one or more webs of non-woven fabric. Typical constructions of this type combine one or more webs of spunbond fabric with a web of meltblown fabric. Such constructions are termed spunbond-meltblown (S-M) and spunbond-meltblown-spunbond (S-M-S) fabrics. A problem arises in the bonding process for such constructions stemming from the relatively high temperatures needed to bond the spunbond material. These temperatures may cause partial melting of the much finer fibers that make up the meltblown web, resulting in pinholes which compromise the barrier properties of the fabric.
It is known that a PP having a high level of solubles can improve process performance in non-woven fabrics, providing lower bonding temperatures and a wider bonding window. It is, however, a burden to PP manufacturers to produce high solubles because large amounts of unwanted wide-spec materials are generated to reach targeted high solubles. Also, it is known that the solubles are responsible for smoke generation during fiber spinning.
It would therefore be desirable to provide a polypropylene material that provides the wide bonding window and low bonding temperatures of a high solubles material without the drawbacks of large amounts of off-spec material and increased smoke generation in processing.